Step-varied r-f tuner



Dec. 22, 1959 J. 5. PRICHARD 2,918,637

STEP-VARIED R-F TUNER Filed April 5, 1957 n. IIII n United States Patent STEP-VARIED R-F TUNER John S. Prichard, Freeport, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application April 5, 1957, Serial No. 651,120

1 Claim. (Cl. 333-82) The present invention relates to high frequency electronic resonant circuits and more particularly to novel and improved apparatus for tuning sections of a transmission line to resonance at selected high frequencies.

In various types of high frequency electronic circuit applications, it often becomes necessary and desirable to rapidly tune the inductance and capacitance of a tank circuit in discrete steps through a predetermined schedule of resonant frequencies. At high frequencies the ordinary inductance of a transmission line and its distributed capacitance to ground conveniently provides the essential inductance and capacitance of a tuned circuit. Moreover, in order to vary the resonant frequency of such a tuned circuit, the effective length of the transmission line need only be properly changed. Although transmission lines of selected effective lengths have been used in the past to provide a tuned resonant circuit at a selected frequency or group of frequencies, considerable difiiculty has been experienced heretofore in providing such apparatus which is tuneable in discrete steps at a comparatively high rate.

Accordingly, it is a principal object of the present invention to provide novel and improved apparatus for rapidly tuning a transmission line type tank circuit to a preselected group of discrete resonant frequencies.

It is a further object of the present invention to provide a novel and improved high frequency tuned circuit which is characterized by a particularly low line loss.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is a perspective view of one preferred embodiment of the present invention.

Figure 2 is a perspective view of another preferred embodiment of the present invention.

Figure 3 is a schematic view of a particular circuit in which the embodiment of Figure 2 finds useful application.

A preferred embodiment of the present invention is illustrated in Figure 1 of the drawing. As shown therein the two-wire balanced transmission line includes conductors 3 and 4 mounted in any suitable manner within the brass shielding box or the like 5. The yoke shaped members 6 which are secured in any suitable manner to the exterior surface of the shielding box 5, extend upwardly therefrom and are spaced along the exterior of the box in any suitable preselected manner. The actuating arms 7 are preferably pivotably positioned in the yokes of the members 6 as shown and extend transversely across the width of the shielding box 5. The plunger elements 8, which are preferably constructed of Bakelite or any other suitable conventional electrical insulating material, are slideably positioned in apertures 9 in the shielding box and are normally biased by the spring members 10 secured thereto upwardly toward their re spective pivoted actuating arms 7. The adjusting screw 2,918,637 Patented Dec. 22, 1959 ICC or the like 11 which extends through each actuating arm 7 engages the upper extremity of its associated plunger 8 and provides an adjustable mechanical link therebetween.

Leaf spring members or the like 12 are secured to the lower cxtermities of the plunger members 8 and provide low resistance electrical paths or short circuits between conductors 3 and 4 when the coin silver contacts 13 and 14 thereof engage the peripheral surfaces of conductors 3 and 4. The shaft member 15 is mounted for rotation in the journal members 16 and 17 and is driven in any suitable conventional manner such as by means of the synchronous electric motor or the like 18.. The cam elements 19, which are mounted on the shaft 15, are constructed and positioned thereon so as to engage and depress the various actuating arms 7 in any suitable preselected timed sequence.

Although the driving mechanism for the shaft 15 is described herein as being a synchronous motor, it is to be understood that any other type motor or any other suitable mechanism which will rotate or oscillate shaft 15 in a predetermined manner could be used without departing from the spirit or scope of the present invention.

Another preferred embodiment of the present invention is illustrated in Figure 2 of the drawing. As shown therein, the tunable unbalanced transmission line includes the inner conductor 31, which is centrally mounted by the insulated supporting means 47 or the like within the shielding box 32, and the grounded conductor strip 33 which is secured along the inner surface of the shielding box 32. The generally L-shaped contact spring element 34, which is preferably secured to the inner conductor 31 in any suitable manner, extends transversely through the aperture 35 in the shielding box 32 and is positioned with respect to the conductors 31 and 33 of the transmission line such that the integral silver coin contact element 36 affixed thereto normally engages the upper edge of the conductor 33. The stop element or the like 37 which is constructed of Bakelite or any other suitable electrical insulating material is secured to the contact spring 34 in any suitable manner and extends upwardly from the upper surface thereof. The relay device or the like 38 is preferably secured to the exterior surface of the shielding box 32 as shown and includes the energizing coil 39, the pivoted armature assembly 40, the switch actuating arm 41, and the armature return spring 42. The energizing circuit for the relay coil 39 extends from the energy source 43 through the switch or the like 44 and the coil back to the energy source. Movement of the armature of switch 44 between its open and closed positions is controlled by any suitable conventional mechanical, electro-mechanical or electronic control mechanism 45. It has been found that this embodiment of the present invention is particularly useful in any high frequency electronic circuit where the schedule of desired resonant frequencies of the tuned transmission line is particularly complex, where it follows no particular cycle of repetition, or where the transmission line must be step tuned from one resonant frequency to the next resonant frequency at a very high rate.

The oscillator circuit of Figure 3 of the drawing illustrates a typical application of the above described high frequency tuned circuit. The plate circuit of the oscillator triode V1 extends from the positive 300 volt supply line 21, through the plate R.F. choke L1, the tube, and the cathode RF. choke L2 to ground. Adjustable condenser C1 is connected as shown between the plate and cathode of triode V1 in parallel with the series connected plate to grid and grid to cathode interelectrode capacitances C2 and C3. The load resistor R1 is coupled to the triode plate grid terminals through appropriate blocking condensers C4 and C6 by a pi-connected impedance matching network. The input capacitance of this network is the plate-to-grid capacitance C2, the series inductance is the high frequence tuned circuit 22, and the output capacitance is the adjustable condenser C5. The grid of triode V1 is connected through the grid R.F. choke L3 to a suitable grid biasing source 23.

It is to be understood that the oscillatorvcircuit of Figure 3 is disclosed herein only to illustrate the manner in which the various embodiments of the present invention find ready application in the art, and that the embodiment of the above described Figures 1 or 2 could be used in any other suitable high frequency oscillator circuit or any other high frequency electronic circuit where a variable tuned circuit is useful. In the operation of the circuit of Figure 3 as the grid end of the tuned circuit goes negative, the plate current through triode V1 is reduced and the positive potential of its plate increases. This increase in positive potential at the plate of triode V1 passes through condenser C4 and the load impedance of resistor R1 and condenser C5 and charges the capacitance C7 of the transmission line to ground positively and therefore provides the oscillator with the necessary positive feedback to sustain oscillations. The operating frequency is of course determined by the inductance of the transmission line and its capacitance to ground. By proper design of the various cam members 19 on shaft 15 and/or by suitable control of the speed of motor 18, the effective length and inductance of the transmission line and therefore the operating frequency of the oscillator may be step-tuned or swept readily through a predetermined schedule of frequencies in a predetermined manner.

It is to be understood that although only a pair of short circuiting devices for the transmission line are shown in the embodiment of Figure 1 and but one such device in the embodiment of Figure 2, any greater or lesser number of the same could be used without departing from the scope or spirit of the present invention.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

Apparatus for tuning a two conductor transmission line to resonance at selected high frequencies said apparatus comprising an electrical shield inclosing the transmission line; a plurality of low impedance leaf spring elements disposed within the electrical shield at predetermined points along the transmission line; a plunger member for each leaf spring element, one end of each plunger member being secured to its respective leaf spring element, the other end of each plunger member extending through an aperture in the electrical shield; an actuating arm for each plunger pivotably mounted on the exterior of the electrical shield and arranged to engage the other end of its respective plunger member; means normally biasing each plunger member and its attached leaf spring element outwardly through its aperture in the electrical shield and out of engagement with the conductors of the transmission line; a synchronous motor; a cam shaft mounted on the electrical shield and mechanically coupled to the motor; and a plurality of cams mounted on the cam shaft, each cam being disposed on the cam shaft so as to at times engage an individual actuating arm and depress the actuating arm and its associated plunger member such that the attached leaf spring element short circuits the conductors of the transmission line.

References Cited in thefile of this patent UNITED STATES PATENTS 1mm Nov. 27, 1951 

